More often than I care to admit, “Talk to Me” reminded me of the Howard Stern bio-pic, “Private Parts.” Only, instead of lesbians and Baba Booey, “Talk” offers social upheaval and instants of comedy that would make Don Knotts exclaim, “That’s a little too broad.” It’s a peculiar, persuasive take on a radio icon, yet it’s barely held together long enough to fill two hours.

Ralph Waldo “Petey” Greene (Don Cheadle) was a hustler and a convict who held a gift for radio that saved him from the hell behind bars. Released in the mid-60s, Greene took his act to the Washington D.C. R&B station WOL to impress uptight program director Dewey Hughes (a wonderful Chiwetel Ejiofor). Hitting the airwaves with his boundary-pushing candor, Greene was an instant smash in the depressed community, starting him on a long career of fame and controversy before the entertainment world became too much pressure for him for bear.

“Talk to Me” see-saws between rambunctious urban comedy and soulful attempts to address what Greene meant to his listeners. I cheer director Kasi Lemmons’s efforts to pick a starting point midway into Greene’s life, eschewing the labor of having to build this personality from childhood. It gooses the energy of the film, at least in the first half, resulting in rollicking, undeniable entertainment. Witnessing Greene’s ascension from ex-con to top radio dog is a rocket of humor and confident direction of personal growth. Lemmons also assigns just as much screentime to Hughes and his frustration with Greene as they rise to prominence together.

Inherently, this is a story of a radio master, and “Talk” is very organized and cautious when presenting Greene on the air. The picture allows the audience a chance to feel Greene’s confrontational style and his marriage to mischief, upsetting his Caucasian boss (Martin Sheen, in full whitey mode), his girlfriend (a piercing Taraji P. Henson), and his competition (Vondie Curtis-Hall and Cedric the Entertainer). The moments with Greene in front of a microphone, sucking in countless cigarettes and searching his mind for the next shred of wisdom, are where “Talk” reaches remarkable glimpses of clarity and feels the most relaxed in tone and execution.

The second half of the picture charts Greene’s rise in respectability, brought on by the way he counseled his audience on the chaotic night Martin Luther King Jr. was assassinated. From there, Hughes and Greene take their careers into their own hands: Greene is pushed onto to the stage, television, and charity events to spread his message of truth with a chaser of comedy. Lemmons struggles to condense the years, and “Talk” loses its spunk in the pursuit of historical legitimacy. With Greene battling the bottle, blowing a “Tonight Show” appearance, and losing his faith in Hughes (who then takes up his own DJ career), the picture starts to feel cramped, in a rush to get to Greene’s death in 1984 to lend the matter some profundity after cracking wise for most of the feature. It’s a little deflating.

No matter the tonal peaks and valleys, “Talk to Me” brings Greene’s attitude to the big screen with confidence, led by Cheadle’s amazing performance. It’s a peek at a mad genius, a cultural buttress, and a preoccupied mind; a man who changed how the radio game was played, paving the way for the airwaves we know today.